When to use the fresh hydrogen return line during the wax oil hydrogenation process
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When should the fresh hydrogen return line be used during the wax oil hydrogenation process?
1. It can be used to regulate the pressure in the reaction system; when the pressure in the reaction system rises, the new hydrogen return line is slightly opened, allowing some of the hydrogen gas exiting from the system to flow back to the inlet of the new hydrogen compressor, thereby balancing the system pressure； 2. Additionally, at the beginning of operation, when raising the pressure in the reaction system and the pressure of the fresh hydrogen is insufficient, the fresh hydrogen return line can be slightly opened to compensate for the pressure at the inlet of the fresh hydrogen compressor, thereby achieving the goal of increasing the pressure in the reaction system.
If it is centrifugal, it also has a surge prevention function. The second point isn’t correct; it should be to prevent an excessive compression ratio from causing mechanical damage. Therefore, the pressure at the inlet is increased through the return line in order to reduce the compression ratio.
Explanation regarding the second point: Our unit is used for the hydrorefining of coker diesel and gasoline. After each shutdown for maintenance and before restarting, due to insufficient pressure in the hydrogen pipeline network, or because the amount of hydrogen available for our unit is only 1000 NM3/H, in order not to affect the unit’s operation, we open fully the connection lines at the inlet and outlet of the new hydrogen compressor (reciprocating type) before starting it. Once it is operational, we gradually close these connection lines until the hydrogen consumption reaches 1000 NM3/H; meanwhile, the pressure in the reaction system is increased slowly, so as to prevent the overall pressure in the hydrogen pipeline network from dropping and affecting the operation of other units.
What a large device, with such low hydrogen consumption
It has two main functions: 1. Adjusting the amount of hydrogen based on system pressure to reduce energy consumption; 2. Regulating the pressure at the compressor inlet to control the compression ratio (the primary function).
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